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Using Empirical Evidence, critically discuss the extent to which Human Intelligence is innate



Intelligence is one of the cores yet complex characteristics of human beings. For a long time, philosophers, psychologists and biologists have been trying to define the nature of human intelligence. They all have found it challenging. Therefore, there are several definitions of intelligence in Psychology. But, the most universal explanation among researchers is (Gottfredson, 1997) “Intelligence is a very general mental capability that, among other things involves the ability to reason, plan, solve problems and think abstractly, comprehend complex ideas, learn quickly and learn from experiences. It is not merely book learning, a narrow academic skill or test-taking smarts. Rather it reflects a broader and deeper capability for comprehending our surroundings- ‘catching on ‘making sense of things or ‘figuring out what to do”.

So, scholars have interpreted intelligence as a mental ability of human beings that helps to adapt to the environment. The human brain is a product of evolution along with other parts of the body. It has also been proved that genetics has an impact on human physiological differences. So, the chances of the brain mechanisms that underlie intelligence being affected by genetics are high. Nonetheless, earlier deterministic genetic explanations of intelligence aroused suspicion. It portrayed intelligence as a limited capacity of human beings. But later theories were based on probabilistic assumptions rather than the deterministic assumption. Now, advanced genetic research has surpassed the notion of nature and nurture debate in the arena of intelligence. They followed several research methods like developmental change, relationships between different cognitive functions and the interplay between nature and nurture. Researchers can identify the genetic factors responsible for intelligence. Thus, researchers have argued whether intelligence is innate or acquired over the entire life span. Therefore, it is debatable to what extent human intelligence is innate. But there is ample experimental evidence that human intelligence is innate to a certain extent. This will be discussed in this article.


In the initial phase of defining intelligence, Spearman first discussed human intelligence as a combination of two factors. One is general or g and the other one is specific or s.  General intelligence refers to the shared mental energy in all kinds of tasks. He stated that the amount of g is limited in a human being. It also depends on the inborn cerebral energy of a human. Intelligence varies from individual to individual as the g factor varies (Spearman, 1914). Later, a noted educational psychologist Arthur Jensen first discussed that the variance in human intelligence could be the variance in g factor that was mostly genetic. He validated this view by summarising the intelligence research. At that time there was a notion that blacks are less intelligent than whites. Jensen showed in his research that the variability in intelligence can be because of the g factor (Jensen, 1996). This view was severely criticised by other psychologists later. They questioned the validity of Jensen’s research. Then started the progression of quantitative and molecular genetics that helped to estimate the impact of innate and acquired factors on human intelligence (Jensen, 2011).

Family resemblance studies: –

If heredity plays an important role in intelligence, members of a family would show similar IQ scores. This hypothesis inspired investigators to do the family resemblance studies. In a study, (Rautiainen et al., 2016) computed the correlation coefficient of IQ scores between the family members. They found that the correlation coefficient for identical twins was the highest. Consequently, the correlation coefficient between parents and children, brothers and sisters, and half-siblings showed less coefficient correlation. From this study, they concluded that heredity affects one’s intelligence significantly.

Davis and his colleagues conducted another study. They took siblings and individuals who did not know each other. Results from this study showed that there was a low correlation in IQ scores of unrelated individuals and a high correlation in the IQ scores of siblings.

Further evidence of IQ resemblance among family members can be seen in the studies reported by Ill and his colleagues. They demonstrated a high correlation between the IQ scores of adopted children and their biological parents. But, the correlation in the IQ scores of adopted children and adopted parents were low (Davis et al., 2014).

From the above-mentioned studies, it can be concluded that individuals having blood relationships have a probability of showing similar IQ scores in an intelligence test.

Twin Studies: –

The genetic structure in twins is similar to other siblings. However, there are identical twins and fraternal twins. The gene structure in identical twins is the same. Hence, the heredity potential in identical twins is higher than fraternal twins who have varied genetic structures. Numerous studies have been conducted by detaching twins at birth and their rearing in various atmospheres (Wixson, 1958).

In one study Wixson took 200 twins. He then attempted to test their IQ on an intelligence scale at different ages. He found that IQ scores of identical twins were related. This was not found on fraternal twins (Wixson, 1958).

In another study, Bouchard and his colleagues planned another design. They searched for twins who were identical and reared in various homes after their birth, away from their home.  He then measured their intelligence. IQ scores of identical twins reared apart showed almost the same IQ as identical twins reared together. He also found that identical twins who reared apart showed similar human characteristics like attitude, bodily appearance, interest aptitude (Wixson, 1958).

Comparing the results of different intelligence studies, it has been stated that identical twins showed an average intelligence of about .80 and fraternal twins showed 0.60. Therefore, twin studies revealed the greater impact of inborn genetic structure on human intelligence (Bouchard, 2009).

Adoption Studies: –

Adoption studies are another type of research. These studies revealed the impact of genetic factors more effectively than the above-mentioned twin studies. Though, adoption studies have not been conducted hugely because researchers have to control so many variables like age, socio-economic background, education, home environment and other things. They cannot randomly assign intelligence tests to subjects. Researchers wanted to check the correlation in the IQ scores between the adopted children and their real parents. Surprisingly, results revealed a high correlation between the intelligence score of adopted children and their real parents. The correlations with rearing parents stood at a minimum. Even, in some cases, it was near-zero especially as children grow older (Mackintosh, 2011).

But other theories show that if the environment in the home of adopted children is good, there is an improvement of intelligence score and performance. Even if they have a good educational opportunity, their IQ score increases significantly in early adulthood (Kendler et al., 2015). These findings have been replicated time and again while considering whether human intelligence is innate or acquired.  Although, it indicates that the environment of the adoptive home has a role in shaping the children’s intelligence over time and this finding may seem to contradict the previous data in any way but that is not the case. Heritability data itself suggests that human intelligence is not entirely the effect of a human’s genetic structure. It also depends on the environment to some extent. Both play an important role.

Mixed Studies:-

Researchers sometimes adopt the mixed-method design. They combine the purpose of twin and adoption studies. Here, researchers focus on identical twins who are separated from their biological parents and brought up in different places. Everyone is put up individually in a varied household and exposed to a lot of different circumstances. One twin often is not aware of another sibling. It has been found the correlation of 0.77 in 13 pairs of identical twins who are brought up apart. Hence, the result suggested a strong genetic influence on human intelligence (Wixson, 1958).   

Later, influenced by these studies, researchers all around the world started investigating with large samples. The IQ scores of identical twins in their research were raised to .75 (Plomin & Von Stumm, 2018). In Brut’s research, he investigated several studies using identical twin pairs with different sample sizes. After interpreting the results, he concluded that the average value for identical twins was increased together significantly (Arslan & Penke, 2015). While comparing these findings with the results of the IQ scores of fraternal twins, the average correlation was found to be 0.60. Hence combining twin and adoption studies, researchers concluded that human intelligence is certainly influenced by genetic and other innate factors (Wixson, 1958).

Recent studies of molecular genetics: – Modern scientific equipment drive its progress rapidly. When DNA Technology developed, scientists started hunting for genes responsible for human intelligence. The search was started by manipulating the genetic structure in animals. When investigators saw the positive results, they tried to replicate them in humans. They collected the DNA samples from different groups related to Intelligence tests. Then they fragmented them into small pieces to identify the genes effectively. From the results, they compared those fragments from high and low IQ groups. The strategy is time-consuming and costly (Scherz, 2021). Therefore, researchers are trying all around the world to do it in a new way. Some significant findings are stated

below: –

  • Rietveld and his colleagues investigated using two large samples. Results showed the correlation in the IQ scores of individuals with variables like education level and g factor. From the first sample, they interpreted that educational background has an impact on the intelligence level. From the second sample, they interpreted that there is a high correlation in the IQ scores of individuals having related DNA sequences (Deary, 2006).
  • Hill and his colleagues investigated among 3511 individuals by analysing the genome sequences. They hypothesised that genes that are present in postsynaptic functioning have an impact on the intelligence level. Findings suggested that individual differences in the intelligence level are due to the variation in the genetic structure in postsynaptic functioning (Hill et al., 2014).
  • (Davis et al., 2014) demonstrated the effect of genes on one’s intelligence level with the help of his colleagues. They also focused on various molecular proteins that are associated with brain size and evolution. Through the study, they showed that few proteins and brain size has a significant impact on the level of Intelligence. It also affects the performance of an individual.
  • Another study was conducted by (Scherz, 2021) using a different approach. He found that genes that are associated with Alzheimer’s disease have an impact on Intelligence level.

Throughout the world, researchers are trying to find the genes that are responsible for the intelligence level. They are discovering new techniques. From all the above-mentioned studies, it can be concluded that a particular genome sequence has an impact on the level of intelligence. Different genes may work collectively to influence the level of intelligence. Researchers are trying to investigate those genes collectively. But it is quite clear that genome sequences and intelligence levels are highly related.

Neuroanatomical Influence on Intelligence:-

Researchers have found that the physiology of the human brain has an important contribution in determining the intelligence of a person. With the advent of recent advanced neuroimaging techniques, scholars have found the brain regions that affect the level of intelligence. From 1988 to 2006, biologists revealed surprising facts about the human brain. It was proved that the frontal lobe alone does not contribute to intelligence, rather the distributed neural networks affect it.

 Even glucose metabolism and intelligence scores were inversely correlated. Hence, many researchers concluded that efficient information flow can cause higher intelligence. Differences in brain function have an impact on the difference in human intelligence. Thus, it can be concluded that the anatomical structure of the brain has an impact on determining intelligence (Fernandes et al., 2020).


All the outlined studies illustrated how human intelligence is innate to a certain extent. Despite empirical evidence of human intelligence being innate to a certain extent, there is no doubt that environmental factors affect the areas of human abilities where intelligence has a role to play. Epigenetics is a new field that describes to what extent human intelligence is a product of nature and nurture. Hence, researchers are relying more on the data found in different epigenetics research. It can be concluded that understanding the interplay between nature and nurture that influence human intelligence together is very important.


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Bouchard, T. (2009). Genetic influence on human intelligence (Spearman’sg): How much?. Annals Of Human Biology36(5), 527-544.

Davis, J., Searles, V., Anderson, N., Keeney, J., Raznahan, A., & Horwood, L. et al. (2014). DUF1220 copy number is linearly associated with increased cognitive function as measured by total IQ and mathematical aptitude scores. Human Genetics134(1), 67-75.

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Fernandes, H., Peñaherrera-Aguirre, M., Woodley of Menie, M., & Figueredo, A. (2020). Macroevolutionary patterns and selection modes for general intelligence (G) and for commonly used neuroanatomical volume measures in primates. Intelligence80, 101456.

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Hill, W., Davies, G., van de Lagemaat, L., Christoforou, A., Marioni, R., & Fernandes, C. et al. (2014). Human cognitive ability is influenced by genetic variation in components of postsynaptic signalling complexes assembled by NMDA receptors and MAGUK proteins. Translational Psychiatry4(1), e341-e341.

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Jensen, A. (2011). The theory of intelligence and its measurement. Intelligence39(4), 171-177.

Kendler, K., Turkheimer, E., Ohlsson, H., Sundquist, J., & Sundquist, K. (2015). Family environment and the malleability of cognitive ability: A Swedish national home-reared and adopted-away cosibling control study. Proceedings Of The National Academy Of Sciences112(15), 4612-4617.

Mackintosh, N. (2011). IQ and human intelligence. Oxford University Press.

Plomin, R., & von Stumm, S. (2018). The new genetics of intelligence. Nature Reviews Genetics19(3), 148-159.

Rautiainen, R., Räty, H., & Kasanen, K. (2016). Is children’s intelligence malleable? Parental perspectives on implicit theories of intelligence. Nordic Psychology68(4), 233-243.

Scherz, P. (2021). Life as an Intelligence Test: Intelligence, Education, and Behavioral Genetics. Culture, Medicine, And Psychiatry.

Spearman, C. (1914). The theory of two factors. Psychological Review21(2), 101-115. Wixson, R. (1958). The Relative Effect Of Heredity And Environment Upon The Refractive Errors Of Identical Twins, Fraternal Twins And Like-Sex Siblings. Optometry And Vision Science35(7), 346-351.

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